Nature and Properties of C3Hf Natural Antitumor Cytotoxins Directed against Murine Lymphosarcoma Cells

Comparison of the Natural Humoral Antitumor Reactivity of Different Strains of Mice

Normal serum from C3Hf mice showed a complement-dependent cytotoxic reactivity against EL4 lymphoma cells, starting from 2 to 3 months of age, whereas normal serum from BALB/c and C57BL/6J mice became reactive only at a later age. The cytotoxins of normal sera of the 3 strains, as well as of a C57BL antiembryo antiserum studied in parallel, belong to the IgM class. When absorption tests were performed, using a variety of absorbing cells, marked differences were found among the sera, which according to their behavior could be divided in two groups: one group comprises the BALB/c and the C57BL sera, the other group the C3Hf serum from both young and old mice and the antiembryo antiserum. The reactivity of the 3 latter sera seems to be directed against specificities related to an ecotropic N-tropic virus, which on the contrary did not seem to be involved in the reactivity of BALB/c and C57BL sera. The C57BL antiembryo antiserum obtained by immunization with C3Hf embryos behaved differently from the C57BL normal serum and similarly to the C3Hf normal serum.

Natural Antilymphoma Antibodies in C3Hf Mice Serum: Lack of Identity with Autoimmune and anti Murine Leukemia Virus Antibodies

Absorption experiments on C3Hf normal mouse sera followed by cytotoxic tests on EL4 lymphoma cells were done to investigate a possible identity between natural antilymphoma antibodies (NAA) and various types of autoantibodies known to be present in normal mouse sera. Single C3Hf normal sera were also tested both by cytotoxicity on EL4 cells and by radioimmune precipitation assay (RIP) on 125I-labelled AKR ecotropic virus to ascertain whether or not viral antigen are the target structures of the NAA activity. The study provides evidence that NAA coexist with autoanticorpal and antiviral activities although they are distinct entities.

Correlation between the Presence of Natural Antitumor Antibodies and Activation of Mulv Endogenous Virus in Balb/C Mice

Individual 3-month-old or 12-month-old BALB/c mice, as well as 5-month-old nu/nu or nu/ + BALB/c mice, showed a direct correlation between the serum level of natural antitumor cytotoxic antibodies and the capacity of spleen cells to infect SC-1 cells permissive for murine ecotropic viruses. Pooled or individual sera from 3-month-old BALB/c mice, negative for the presence of natural antitumor cytotoxic antibodies and whose spleen cells were unable to infect the SC-1 cells, were negative both for SC-1 cells and SC-1 cells infected by MuLV. On the contrary, pooled or individual sera from 15-month-old BALB/c mice, positive for the presence of natural antitumor antibodies and with infecting spleen cells, were cytotoxic for infected SC-1 cells but not for the uninfected ones. The infection of SC-1 cells by MuLV could be inhibited by 3-month-old spleen cells, and this effect was suppressed by depriving the inhibiting spleen cells of T cells by means of an anti-Thy-1 antibody plus complement. The cells with infectious capacity did not belong to the T-cell compartment, as demonstrated by the lack of infection after passing the infecting spleen cells through an anti-Ig column, whereas T-deprivation did not modify the infectious capacity. A natural anti-gp70 monoclonal antibody, which exerted a complement-dependent cytotoxic effect on tumor cells, stronghly inhibited the infection of the permissive SC-1 cells by MuLV.